The need for improvement in rapid processing suitability of silver halide photographic materials is still strong in the photographic industry.
In the developing processing of silver halide photographic materials after imagewise exposure, these materials are usually subjected to continuous processing with an automatic developing machine installed in a photofinishing laboratory. As a means to render an acceptable service to users, for instance, it has been required that the photographic materials be developed and returned to the user thereof in the course of the day of their acceptance. Recent years have made even a request that the photographic materials be developed and returned to the user thereof within one hour after acceptance. Thus, the rapid processing is of ever-increasing necessity. Further, since reduction in processing time increases efficiency and diminishes cost of output, this point also constitutes an important factor in the need for urgent development in the rapid processing arts.
Under these circumstances, the shape, the size and the composition of silver halide emulsion grains used in a photosensitive material are known to have great influences upon the development speed and so on. For instance, it is known that the development proceeds at a higher speed the smaller is the emulsion grain size or the higher is the chloride content in silver halide emulsion grains. Therefore, it becomes important to make efficient use of those factors in designing rapid processable photographic materials.
In order to avoid lowering the sensitivity as far as possible in a case of using silver halide grains reduced in size, it is desirable that the amount of spectral sensitizing dyes adsorbed to silver halide grains be set at a high level. Since the surface area per volume of each silver halide grain increases proportionally to reduction in size of each silver halide grain, it is required to use spectral sensitizing dyes in a greater amount the smaller the silver halide grains used are in size. Further, it is known that, as they are greater in surface area per volume than isotropic grains, tabular silver halide grains can increase the quantity of spectral sensitizing dyes adsorbed thereto to gain an advantage in the achievement of high sensitivity over isotropic grains. Accordingly, it is a difficult problem to avoid increasing the amount of spectral sensitizing dyes used in the case where despite using silver halide grains having the smallest possible size so as to have an advantage in rapid processing suitability, the acquisition of high sensitivity is intended.
However, it is also known that such an increase in the amount of sensitizing dyes used poses new problems. In particular, the color stain due to spectral sensitizing dyes remaining in a photosensitive material after photographic processing (the so-called residual color) constitutes an obstacle to the speedup of photographic processing. Because of this residual color problem, a contradiction is incurred between the difficulty in using silver halide grains with a small size and the advantage of rapid processing suitability obtained from the use thereof.
It is disclosed in JP-A-6-230501 (the term "JP-A" as used herein means an "unexamined published Japanese patent application") that the aforementioned drawback of causing residual color can be mitigated by using a spectral sensitizing dye having as a substituent an aromatic group having a special structure, other than a phenyl group, in a silver halide photographic material.
As a result of extensive investigation, it has been confirmed that the residual color in a photosensitive material was reduced by the use of the spectral sensitizing dye disclosed in the above-cited patent. Although the residual color became less than those caused by conventional phenyl group-containing dyes so long as the dye disclosed in the above-cited patent, which had as a substituent the aromatic group of a specified structure, was used, it couldn't be said that the residual color problem was solved completely, but the photosensitive material still suffered coloration due to the sensitizing dyes remaining in the unexposed area after photographic processing. The coloration problem caused by the residue of spectral sensitizing dyes became serious particularly in the case of using small-size or tabular silver halide grains having a great surface area per volume, whereto a large amount of dyes are adsorbed, provided that the amount of dyes used per surface area is set at the same value, compared with other cases. Further, it turned out that this coloration problem became a great obstacle to the reduction of processing time for the speedup of photographic processing.
As a result of further extensive investigation, on the other hand, it has been also confirmed that the foregoing residual color problem was able to be solved more effectively by the photosensitive materials using the sensitizing dyes free from the features of the above-cited patent, i.e., the sensitizing dyes having such a structure as to contain no aromatic group as a constituent. However, such photosensitive materials, as disclosed in comparative examples in JP-A-7-5614, were unable to withstand practical use because of their serious drawback of causing a sensitivity drop upon storage prior to exposure.
As far as conventional arts are used, it is therefore very difficult to obtain a silver halide photographic material having much less residual color than ever, being inhibited from lowering its sensitivity during the storage prior to exposure and having rapid processing suitability.